This paper forms the introduction to my forthcoming book, 'Authorities'. The book suggests that interactions between state, international, transnational and intra-state law involve overlapping, and sometimes conflicting, claims to legitimate authority. These have led scholars to new theoretical explanations of sovereignty, constitutionalism, and legality, but there has been no close attention to authority itself. The book asks whether, and under what conditions, there can be multiple legitimate authorities with overlapping or conflicting domains. Can legitimate authority be shared between state, supra-state and non-state actors, and if so, how should they relate to one another?

This introduction explores the puzzles presented by plurality of authority and outlines the approach and arguments presented in the book. It situates the project within a broader challenge posed by pluralist jurisprudence, explains what role a theory of authority might play in addressing that challenge, and introduces key illustrations of inter-authority relationships from constitutional, international, indigenous and transnational law.